1. Field of the Invention
The present invention generally relates to a lens system for correcting vision in the eye. More specifically, the present invention generally relates to an intraocular lens system (IOL), which can be implanted in the anterior or posterior chambers of the eye in place of or in addition to the natural lens, or which can be implanted as piggyback IOL lens on the natural or artificial lens in the eye, for correcting presbyopia.
2. Description of the Related Art
A normal ametropic eye includes a cornea, lens and retina. The cornea and lens of the normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disease known as macular degeneration which can greatly degrade vision.
Macular degeneration has become one of the leading causes of blindness in adults. This disease affects the central retinal area known as the macula, which receives light focused by the cornea and lens and acute vision. Macular degeneration can lead to a gradual or sudden loss of vision to the level of 20/200 or less. Commonly, loss of vision only affects the central retinal area of about 0.25 to 4 square millimeters, and does not usually progress beyond this area, thereby leaving 95-99% of the retina unaffected. Thus, reading and driving vision can be lost, while peripheral vision remains intact.
U.S. Pat. Nos. 4,666,446 and 4,581,031, both to Koziol and Peyman, and both of which are incorporated by reference herein, each disclose intraocular lenses which are implanted in the eye in place of the natural lens to redirect the rays of light to minimize the adverse affect on vision caused by the macular degeneration of the eye. For example, U.S. Pat. No. 4,666,446 discloses an intraocular lens comprising a first portion including a diverging lens and a second portion including a converging lens. The converging lens provides the eye with substantially the same focusing ability of the natural lens prior to implantation of the intraocular lens. Thus, the eye will have decreased visual acuity due to the macular degeneration, but will also have unrestricted peripheral vision. The diverging lens, on the other hand, when combined with a converging lens positioned outside of the eye (e.g., a spectacle lens), provides a magnified image with increased visual acuity but a restricted visual field. Therefore, this type of intraocular lens creates a teledioptic lens system, which provides the patient with the choice of unmagnified but peripherally unrestricted vision or magnified but peripherally restricted vision.
U.S. Pat. No. 4,581,031 discloses an intraocular lens including a convex portion and a prismatic portion. The combined convex/prismatic lens directs rays of light away from the center of the retina that has been damaged by macular degeneration, and focuses those rays onto an undiseased area of the retina, thus providing greater visual acuity.
As discussed above, U.S. Pat. Nos. 4,666,446 and 4,581,031 clearly disclose that it is known to use particular types of intraocular lenses in place of the natural lens to reduce the adverse affect of macular degeneration on vision.
U.S. Pat. Nos. 5,098,444, 5,366,502, 5,358,520, and 4,932,971, as well as world patent application WO 94/07435, the entire contents of these documents being incorporated by reference herein, each disclose that it is known to attach a supplemental intraocular lens to an existing artificial intraocular lens to correct for ongoing degradation of vision. That is, if the ability of the eye to focus grows worse over time, instead of replacing the entire intraocular lens with a new intraocular lens having a different refractive power, a supplemental intraocular lens can be attached to the existing intraocular lens. This technique is less invasive and hence, less traumatic to the eye.
U.S. Pat. No. 6,197,057, the entire contents of which are herein incorporated by reference, relates to a lens system that combines a high plus lens with a plus and minus intraocular lens (IOL), so that the lens system works in a manner similar to a Galilean telescope. Generally, as shown in FIGS. 1 and 2 of the '057 patent, the high plus lens is outside the eye (i.e., in glasses or spectacles, or in a contact lens) and the plus and minus lens is an IOL that replaces or works in conjunction with the natural lens of the patient.
Additionally, if desired, the plus and minus lens can have a high minus portion in the center of the eye, while the portions surrounding the minus portion have no or substantially no refractive power, that is, the surrounding portion can be flat or substantially flat.
The Peyman '057 patent also discloses a supplemental intraocular lens that can be attached to the natural lens or an existing artificial lens to make the lens adaptable to function as a teledioptic or diffractive prismatic lens of the type described above.
Presbyopia, which is blurred vision of close up objects, for example, objects positioned for reading, typically occurs due to aging of the eye. A conventional method for correcting the refractive error in a cornea is keratophakia, that is, implantation of a lens inside the cornea. Keratophakia uses an implant which is placed into the cornea approximately equidistant from the exterior and interior surfaces of the cornea. The procedure is usually done by first preparing a lens from corneal donor tissue or synthetic material using a cryo-lathe. The lens is implanted by removing a portion of the cornea with a device called a microkeratome, and the tissue is sutured back into place over the lens. However, problems can arise when microkeratomes are used for cutting the cornea. First, irregular keratectomies or perforations of the eye can result. Second, the recovery of vision can be rather prolonged.
Another surgical technique exists that uses a femtosecond laser to separate layers inside the stromal portion of the eye, at least two-thirds of the distance from the top surface of the cornea to the inside of the eye. An incision is made to access this area and a solid inlay is inserted to help correct myopia in the eye. By separating the layers in the bottom two-thirds of the stromal portion, it is difficult to access the separated area to insert the inlay and virtually impossible to change or modify the inlay without another extensive surgical procedure. This procedure requires making an incision which is parallel or substantially parallel to the visual axis and is limited in the lateral direction by a maximum size of 0.3 mm to encase a relatively rigid inlay that forces the tissue in the lateral direction.
Additional surgical techniques exist that use ultraviolet light and short wavelength lasers to modify the shape of the cornea. For example, excimer lasers, such as those described in U.S. Pat. No. 4,840,175 to Peyman, which is incorporated herein by reference, emit pulsed ultraviolet radiation that can be used to decompose or photoablate tissue in the live cornea so as to reshape the cornea.
Specifically, the Peyman '175 patent discloses the laser surgical technique known as laser in situ keratomycosis (LASIK). In this technique, a portion of the front of the live cornea can be cut away in the form of a flap having a thickness of about 160 microns. This cut portion is removed from the live cornea to expose an inner surface of the cornea. A laser beam is then directed onto the exposed inner surface to ablate a desired amount of the inner surface up to 150-180 microns deep. The cut portion is reattached over the ablated portion of the cornea and assumes a shape conforming to that of the ablated portion. Additionally, in the LASIK procedure, a femtosecond laser can be used to cut and separate the flap.
Other conventional methods that have been employed specifically to correct presbyopia have been unsuccessful. Some of those methods include using an excimer laser to ablate the peripheral part of the cornea, expanding the sclera behind the limbus area of the cornea, implanting a plus lens inside the corneal stroma, using a multifocal intraocular lens after removal of the cataractous lens, and using bifocal glasses and bifocal contact lenses.
However, because only certain amount of cornea can be ablated without the remaining cornea becoming unstable or experiencing outbulging (ectasia), this technique is not especially effective in correcting very high myopia. That is, a typical cornea is on average about 500 microns thick. The laser ablation technique requires that at least about 250 microns of the corneal stroma remain after the ablation is completed so that instability and outbulging do not occur. Also, these conventional implants, while correcting a refractive error of the patient, also distort the normal vision of the patient.
Additional methods for correcting the refractive error in the eye include inserting an implant in-between layers of the cornea. Generally, this is achieved using several different methods. The first method involves inserting a ring between layers of the cornea, as described in U.S. Pat. No. 5,405,384 to Silvestrini, the entire contents of which is incorporated herein by reference. Typically, a dissector is inserted in the cornea and forms a channel therein. Once it is removed, a ring is then inserted into the channel to alter the curvature of the cornea. In the second method, a flap can be created similarly to the LASIK procedure and a lens can be inserted under the flap, as described in U.S. Pat. No. 6,102,946 to Nigam, the entire contents of which is incorporated herein by reference. The third method involves forming a pocket using an instrument, and inserting an implant into the pocket, as described in U.S. Pat. No. 4,655,774 to Choyce, the entire contents of which is incorporated herein by reference.
However, with the above described techniques, a knife or other mechanical instrument is generally used to form the channel, flap or pocket. Use of these instruments may result in damage or imprecision in the cut or formation of the desired area in which the implant is placed. Additionally, these conventional techniques do not include determination and testing of an appropriate implant for correcting a refractive error of a particular patient.
Also, prior methods for the treatment of presbyopia have been unsuccessful. One prior method involved implantation of a disc shaped inlay or lens over the central visual axis of the cornea. The disc inlay had a high index of refraction to correct presbyopia and/or hyperopia. However, because the disc covered the center area around the visual axis, the patient's farsighted vision was blurred by the inlay. Another prior method involved a ring shaped inlay implanted around the visual axis. The ring inlay had a lower index of refraction or an index of refraction that is the same as the cornea and therefor corrected myopic refractive errors instead of hyperopic or presbyopic error.
Therefore, there exists a need for an IOL and improved method of correcting refractive error, particularly presbyopia, in the eye, that does not distort the normal vision of the eye, such as far sighted vision. Moreover, there exists a need for selecting the appropriate IOL for correcting the particular refractive error of the patient.